East Asian SO2 pollution plume over Europe – Part 2: Evolution and potential impact 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, 82234 Wessling, Germany
2Max-Planck Institute for Nuclear Physics, (MPIK), Atmospheric Physics Division, P.O. Box 103980, 69029 Heidelberg, Germany
3Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland
4Department of Technology, Metropolia University of Applied Sciences, P.O. Box 4000, 00180 Helsinki, Finland
5Norwegian Institute for Air Research (NILU), Dept. Regional and Global Pollution Issues, Kjeller, Norway
Received: 04 Dec 2008 – Published in Atmos. Chem. Phys. Discuss.: 28 Jan 2009 – Published: 20 Jul 2009Abstract. We report on the first observation-based case study of an aged East Asian anthropogenic SO2 pollution plume over Europe.
Our airborne measurements in that plume detected highly elevated SO2 mole fractions (up to 900 pmol/mol) between about
5000 and 7000 m altitude. Here, we focus on investigations of the origin, dispersion, evolution, conversion, and potential impact
of the observed excess SO2. In particular, we investigate SO2 conversion to gas-phase sulfuric acid and sulfuric
acid aerosols. Our FLEXPART and LAGRANTO model simulations, along with additional trace gas measurements, suggest that the plume
originated from East Asian fossil fuel combustion sources and, 8–7 days prior to its arrival over Europe, ascended over the coast
region of central East Asia to 9000 m altitude, probably in a cyclonic system with an associated warm conveyor belt. During this
initial plume ascent a substantial fraction of the initially available SO2 must have escaped from removal by cloud
processes. Hereafter, while mostly descending slowly, the plume experienced advection across the North Pacific, North America and
the North Atlantic. During its upper troposphere travel, clouds were absent in and above the plume and OH-induced gas-phase
conversion of SO2 to gas-phase sulfuric acid (GSA) was operative, followed by GSA nucleation and condensation leading to
sulfuric acid aerosol formation and growth. Our AEROFOR model simulations indicate that numerous large sulfuric acid aerosol
particles were formed, which at least tempora\-rily, caused substantial horizontal visibility degradation, and which have the
potential to act as water vapor condensation nuclei in liquid water cloud formation, already at water vapor supersaturations as
low as about 0.1%. Our AEROFOR model simulations also indicate that those fossil fuel combustion generated soot particles, which
have survived cloud induced removal during the initial plume ascent, have experienced extensive
H2SO4/H2O-coating, during upper troposphere plume travel. This coating may have dramatically altered the
morphology and markedly increased the light absorption efficiency of soot particles.
Citation: Fiedler, V., Arnold, F., Schlager, H., Dörnbrack, A., Pirjola, L., and Stohl, A.: East Asian SO2 pollution plume over Europe – Part 2: Evolution and potential impact, Atmos. Chem. Phys., 9, 4729-4745, doi:10.5194/acp-9-4729-2009, 2009.